This invention relates to solar energy systems in general and more particularly to solar energy distillation systems.
In U.S. Pat. No. 4,134,393, issued on Jan. 6, 1979, of which I am a co-inventor, in U.S. Pat. No. 4,194,949 issued on Mar. 25, 1980, of which I am sole inventor, in U.S. Pat. No. 4,210,121 issued on July 1, 1980, of which I am sole inventor, and in pending Application Ser. No. 807,513 filed June 20, 1977, now abandoned, of which I am sole inventor, solar energy distillation apparatus are disclosed in which a part of the heat of condensation of the condensing liquid is recovered. In the disclosed embodiments in those patents and in that application, the heat of condensation is transferred to a fluid in a fluid lens disposed over the liquid to be distilled which includes an inclined bottom surface on which the evaporated liquid is condensed and along which the condensed liquid flows to be discharged from the lower end thereof. The '949 and '121 patents and the '513 application also disclose recovering heat from the condensate and from a concentrate (brine) of the liquid being condensed.
It is generally undesirable to incline a fluid lens at more than an angle of about 25.degree. in order to maintain the fluid pressure in the lens at a level which does not require a high pressure lens construction. However, at locations where a lens inclination of greater than 25.degree. is desirable to increase collection, a fluid lens inclined only at 25.degree. operates at reduced efficiency.
In application Ser. No. 915,001, filed June 13, 1978, now U.S. Pat. No. 4,270,981, solar distillation apparatus is disclosed comprising conduit means interposed between lens means for concentrating the solar energy and the liquid to be distilled. Solar energy is concentrated by lens means in the liquid to be distilled through the conduit means. In one embodiment, the conduit means comprise a double plate conduit having an upper and a lower plate between which a heat exchange fluid flows. The concentrated solar energy causes the liquid to evaporate with the vapor impinging and being condensed upon the lower surface of the lower plate of the double plate conduit, the condensed liquid flowing along the lower surface of the lower plate to the lower end thereof and falling therefrom into a container, a substantial part of the heat of condensation of the condensing vapor being absorbed by the fluid in the double plate conduit means.
According to embodiments of Ser. No. 915,001, now U.S. Pat. No. 4,270,981, the lens means comprise a plurality of sets or series of Fresnel-type lenses arranged to provide elongated narrow foci. The container includes a plurality of baffles dividing the container interior into a plurality of distillation compartments for the liquid to be distilled and is inclined so that the compartments are offset in height. The bottom of the compartments containing the liquid to be distilled may be blackened to allow absorption of solar energy and enhance the heating of the liquid. The elongated foci of the lenses may be located in and along a different compartment or they may extend transversely to the compartments.
As disclosed in Ser. No. 915,001, now U.S. Pat. No. 4,270,981, an expansion tank for the heat exchange fluid in the double plate conduit is located so as to provide minimal pressure within the double plate conduit. A heat exchanger is also provided to transfer the heat recovered in the heat exchange fluid circulated in the double plate conduit to the liquid being introduced into the container to preheat the liquid. The heat exchanger is also located to minimize pressure in the double plate conduit.
As disclosed in Ser. No. 44,901, now U.S. Pat. No. 4,323,052, an undulated plate system is provided over which the liquid to be distilled is conducted. A single panel or plurality of adjacent panels made of blackened flexible plastic or the like, such as isobutyl, may be disposed over all or part of the plate system. The panel or panels are attached in the plate system in a removable manner which will permit removal thereof in order that deposits which may form on the panel(s) can be removed.
According to Ser. No. 44,901, now U.S. Pat. No. 4,323,052, it is preferred that the undulated plate system be placed above the focal area of maximum concentration obtained from Fresnel-type lens concentrators. This permits a wider spread of the energy converging from the lenses on the undulated plate system so that a wider area of the plate system is heated. A double plate conduit is interposed between the plate system and the lens. The fluid circulating in the double plate conduit is allowed to spread along the surface of the plates comprising the double plate conduit and is regulated, thus controlling the temperature of the fluid.
According to Ser. No. 44,901, now U.S. Pat. No. 4,323,052, photovoltaic cells can be installed in one or more bottoms or valleys of the undulated plate system at the locations where the energy is concentrated by the Fresnel-type lenses. The photovoltaic cells can be encapsulated in a transparent plastic or glass cover so as to protect the cells from the liquid being distilled. The cells can also be enclosed in a transparent tube in which distilled liquid such as cooled condensate produced by a distillation unit can circulate and further absorb heat generated by the infrared rays. Such a heat exchange can reduce the temperature of the condensate.
Infrared rays can be absorbed by the fluid in the double plate conduit means (Ser. Nos. 915,001, now U.S. Pat. No. 4,270,981 and 44,901, now U.S. Pat. No. 4,323,052, ) by the fluid circulated around the photovoltaic cells (Ser. No. 44,901, now U.S. Pat. No. 4,323,052 and U.S. Pat. No.. 4,134,393) and by the fluid circulated through a fluid lens (U.S. Pat. Nos. 4,210,121 and 4,194,949 and Ser. No. 807,513, now abandoned), for example, to maintain the temperature of the cells lower.
In Ser. No. 44,901, now U.S. Pat. No. 4,323,052 provisions are made to recirculate the liquid conducted over the undulated plate system both during the day and night and on days without sunshine. In the case of distilling sea water, the brine obtained at the output of the distillation apparatus will typically be at a temperature of 80.degree. C. and its quantity will be for instance eight times as large as the water vaporized by solar energy alone. Furthermore, as disclosed in U.S. Pat. No. 4,194,949 and Ser. No. 915,001, now Pat. No. 4,270,981, larger quantities of the fluid carried in the conduit against which the evaporated water condenses are required to maintain condensation and carry away that heat. Through recycling of the brine, salt can be extracted therefrom with an increased salt content after several recyclings.
Ser. No. 44,901, now Pat. No. 4,323,052, also provides for storing the fluid circulating in the conduit means, the brine and the condensate, all in selected quantities, in the space below an insulated panel on which the undulated plate system rests. By storing these fluids beneath the insulated panel, further insulation is provided reducing heat losses.
In the aforementioned patents and applications, either a fluid lens or a conduit disposed between a concentrating lens and the liquid to be distilled is used to condense evaporated liquid, the fluid lens and the conduit means being supplied with a fluid which assists in condensing evaporated liquid.
Typically, when a concentrating lens is used, the lens is oriented to face the sun and can be situated at an angle of 45.degree. , for example. Additionally, while concentrating solar energy, a lens introduces a transmission loss which can be in the order of 20%. To this must be added losses resulting from the structure supporting the lens. Moreover, a lens such as a Fresnel-type lens typically collects only direct solar energy and not diffuse solar energy which can account for about 10% to about 30% of the total irradiation.